1. Field of the Invention
This invention relates to ferulyl-substituted and coumaryl-substituted acylglycerols, their method of preparation through the transesterification of a triglyceride and a ferulic or coumaric ester, and the use of these compounds as sunscreen ingredients.
2. Description of the Prior Art
Health hazards associated with exposure to the sun are well established. The short term effect of excessive exposure to sunlight is erythema, commonly referred to as sunburn. Sunburn is primarily the result of UVB radiation having a wavelength of from about 290 nm to about 320 nm. Long term effects of exposure to sunlight include skin cancer (melanoma) and premature aging of the skin (including wrinkling, loss of elasticity, and pigment changes). These effects are predominantly caused by UVA radiation having a wavelength of from about 320 nm to about 400 nm. Public awareness of the dangers of sun exposure has stimulated the market for personal care products containing sunscreens.
Sunscreens function either as ultraviolet (UV) filters or UV blocks. UV blocks, such as TiO2 and ZnO, as well as derivatives of other metal-oxides, form a physical barrier that scatters UV light (Fairhurst et al., xe2x80x9cParticulate Sun Blocks: General Principlesxe2x80x9d, Sunscreens: Development, Evaluation, and Regulatory Aspects 2nd Edn, pp. 313-352, 1997). These UV blocks offer the most comprehensive sunscreen protection, blocking the full spectrum of UVA (400-320 nm) and UVB (320-290 nm) light. As a result of the particulate nature of these formulations, they often leave a noticeable residue when applied to the skin, which is cosmetically unacceptable to the consumer. The most commonly used sunscreens are UV filters, which are typically organic compounds incorporated at levels of about 2-15% into topical formulations (N. A. Shaath, xe2x80x9cEvolution of Modern Sunscreen Chemicalsxe2x80x9d, Ibid, pp. 3-33, 1997), (N. A. Shaath, xe2x80x9cQuality Control of Sunscreensxe2x80x9d, Ibid, pp. 657-676, 1997). A disadvantage of UV filters is that each organic compound has a limited range of maximum UV absorptivity, rendering each reagent better suited for either UVA protection or UVB protection but not both. The advantage of the UV filtering molecules, however, is that they can be engineered to provide sunscreens with desirable physical appearance, solubility, and water resistant properties (N. A. Shaath, xe2x80x9cQuality Control of Sunscreensxe2x80x9d, Ibid, pp. 657-676, 1997).
Although no longer used today, benzyl cinnamate formulated as an emulsion with benzyl salicylate, was used as a sunscreen as early as 1928 (N. A. Shaath, xe2x80x9cEvolution of Modern Sunscreen Chemicalsxe2x80x9d, Ibid, pp. 3-33, 1997). Today, cinnamic acid derivatives are the most widely used UVB absorbing chemicals in sunscreen formulations, with four derivatives approved for use in the United States and 17 approved for use in Europe (N. A. Shaath, xe2x80x9cEvolution of Modern Sunscreen Chemicalsxe2x80x9d, Ibid, pp. 3-33, 1997). The unsaturated Cxe2x95x90C bond adjacent to the aromatic ring in cinnamates allows for a continuous, conjugated p-system throughout the molecule. An electron can be delocalized throughout the p-system by photo-excitation with energy corresponding to xcx9c305 nm. Most common cinnamic acids and short chain esters are water soluble, limiting their usefulness as waterproof sunscreens. Cinnamic acid derivatives, therefore, have been designed with long chain hydrocarbons (i.e. octyl-p-methoxy cinnamate), which renders them water-insoluble and suitable for waterproof sunscreens. The xe2x80x94OCH3 group of octyl-p-methoxy cinnamate acts as an electron-releasing group to improve the electron excitation process (N. A. Shaath, xe2x80x9cEvolution of Modern Sunscreen Chemicalsxe2x80x9d, Ibid, pp. 3-33, 1997).
There is currently a growing interest in modifying fats and oils to form structured lipids with specific properties for nutritional and pharmaceutical applications. Recent reviews have outlined the strategies for synthesizing tailor-made fats and oils and their desired properties (Willis et al., xe2x80x9cLipid Modification Strategies in the Production of Nutritionally Functional Fats and Oilsxe2x80x9d, Crit. Rev. Food Sci. Nutr. 38:639-674, 1998), (F. D. Gunstone, xe2x80x9cMovements Towards Tailor-Made Fatsxe2x80x9d, Prog. Lipid. Res. 37:277-305, 1998). These strategies have included blending, distillation, fractionation, hydrogenation, interesterification with chemical catalysts, and more recently interesterification with biocatalysts. Chemical interesterifications of triacylglycerols for industrial applications are typically performed using inorganic catalysts at elevated temperatures (200-250xc2x0 C.) (N. N. Gandhi, xe2x80x9cApplications of Lipasexe2x80x9d, J. Am. Oil Chem. Soc. 74:621-633, 1997). Enzymatic interesterifications, however, offer the advantages of milder reaction conditions, a wider variety of synthetic substrates, and regioselective specificity towards the acyl groups of the triglycerols (Schmid et al., xe2x80x9cLipases: Interfacial Enzymes with attractive Applicationsxe2x80x9d, Angew. Chem. Int. Ed. 37:1608-1633, 1998).
We have now discovered lipase-catalyzed reactions are useful for synthesizing ferulyl-substituted or coumaryl-substituted acylglycerols with properties suitable for use as possible sunscreen agents. These agents are readily produced in high yield by means of transesterification of a triglyceride and a ferulic or coumaric ester.
The compounds of this invention are generally characterized by Formula I: 
wherein R1=OCH3 or H; and
wherein R2 and R3 are each independently selected from OH and a C2-C24 fatty acid moiety.
In accordance with this discovery, it is an object of this invention to provide novel ferulyl-substituted or coumaryl-substituted acylglycerols having utility as sunscreen agents.
It is a further object of this invention to provide a facile and efficacious method of producing the subject sunscreen agents by means of a transesterification reaction.
It is also an object of the invention to produce a sunscreen agent that provides broad spectrum UV (UVA and UVB) protection.
Another object of the invention is to incorporate the ferulyl-substituted or coumaryl-substituted acylglycerols of the invention into sunscreen formulations.
A further object of the invention is to produce sunscreen agents that have the advantage of being synthesized from natural materials, while providing a value-added use for vegetable oils.
Other objects and advantages of this invention will become readily apparent from the ensuing description.